DESCRIPTION: (Applicant's Abstract) Our long-term goal is to develop novel biotherapies that will specifically target and destroy residual leukemia. The proposed studies will test the general hypothesis that site-directed gene therapy with hematopoietic progenitor cells, genetically modified to secrete human tumor necrosis factor-alpha (hTNF-a), will significantly increase the destruction of leukemia cells remaining after high-dose chemotherapy/bone marrow (BM) transplantation. Our preliminary data show that administration of hTNF-a secreting progenitor cells following chemotherapy with cyclophosphamide (CY) and BM transplantation dramatically enhances survival (80 percent) of mice inoculated with a lethal dose of 32Dp210 murine myeloid leukemia cells without toxic side effects. We will test the hypothesis that combined therapy with CY, BM-transplant, and TNF-a secreting progenitor cells generates a greater antileukemic effect than is produced by any modality alone. We will accomplish this by the following specific aims: 1) determine the extent to which immunomodulatory effects of CY on T-helper (Th) cells and cytotoxic effector cells (CTLs and NK cells) contribute toward the antileukemic activity of CY/TNF-a gene therapy, 2) identify the cell population(s) within BM-transplant (e.g., T cells, mesenchymal cells or progenitor cells) that enhances the efficacy of combined therapy, and 3) determine whether the mechanism(s) of the antileukemic effect of CY/TNF-a treatment involves: a) augmentation of leukemia antigen presentation by dendritic cells, b) generation of leukemia specific (CTLs) and non-specific (NK cells/macrophages) cytotoxic effector cells, c) production of secondary cytokines with antileukemic activity, and d) the induction of programmed cell death (apoptosis) in leukemia cells. The results of these studies will demonstrate the value of combining this novel approach of site-directed TNFa gene therapy with other commonly used anticancer treatment strategies to achieve maximum destruction of residual leukemia. This would make possible the rapid implementation of this novel treatment strategy to eradicate residual leukemia in humans, without the toxic side effects of systemic TNF-a therapy.